Target displacement detector utilizing an image dissector tube having an aperture through which pass the electrons of the focused electron image



R. sTARER 3,495,087 TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE Feb. 10, 1970 HAVING AN APERTURE THROUGH WHICH PASS THE ELECTRONS OF THE FOCUSED ELECTRON IMAGE Filed Nov. 26, 1965 9 Sheets-Sheet 2 00in/T FIG. Z

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Feb. 10, 1970 R. s'rARER 3,495,087

TARGET DISPLAGEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PAss THE ELECTRONS OF THE FOCUSED ELECTRON IMAGE Filed Nov. 26. 1965 9 Sheets-Sheet 3 /ME ...y N VEN TOR.

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Feb. l0, 1970 R. sTARER 3,495,087

TARGET DTSPLACEHENT DETECTOR UTTLIzTHG AN IMAGE DlssEcToH TUBE HAVING AN APERTUHE THROUGH WHICH PAss THE ELEcTHoNs oF THE FocUsED ELEcTRoN IMAGE Filed Nov. 26, 1965 9 Sheets-Sheet 4 FIG... 7 Lfvsz osfcraf? BYQJEQJ R. sTARER Feb. 10, 1970 TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PASS THE ELECTRONS 0F THE FOCUSED ELECTRON IMAGE 9 Sheets-Sheet 5 Filed Nov. 26. 1965 INVENTOR. aa' AS'drfr, BY

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Feb. 10, 197() R. STARER TARGET DI'SPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PASS THE ELECTRONS 0F THE FOCUSED ELECTRON IMAGE Filed Nov. 26, 1965 9 Sheets-Sheet e I N VEN TOR. 50km? 'zref; B Y

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TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PASS THE ELECTRONS 0F THE FOCUSED ELECTRON IMAGE Filed Nov. 26, 1965 9 Sheets-Sheet 7 I'IG'; l0..

I N VEN TOR.

' TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PASS THE ELECTRONS OF THE FOCUSED ELECTRON IMAGE ofr Sklar,

NM# @ad A 7 701705 YJ.

Feb. 10, 1970 R51-Aman 3,495,087

TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DIssEcToR TUBE HAVING AN APERTURE THROUGH WHICH PAss THE ELECTRONS 0F THE FOCUSED ELECTRON IMAGE Filed Nov. 26, 1965 9 Sheets-Sheet 9 United States Patent G 3,495,087 TARGET DISPLACEMENT DETECTOR UTILIZING AN IMAGE DISSECTOR TUBE HAVING AN APERTURE THROUGH WHICH PASS THE ELEC- TRONS F THE FOCUSED ELECTRQN IMAGE Robert Starer, Rydal, Pa., assignor to Phystech, Incorporated, Elkins Park, Pa., a corporation of Pennsylvania Filed Nov. 26, 1965, Ser. No. 509,786 Int. Cl. H01j 31/50, 39/12: G01j l/20 U.S. Cl. 250-213 Claims ABSTRACT 0F THE DISCLOSURE A device is disclosed for detecting and measuring small amplitude high speed displacement, as for example, vibration of a physical body. An image dissector tube is employed which is focused on the optical discontinuity between the dark and bright portions of the body whose vibration is to be detected. The device does not employ a servo-system technique. There is no feedback from the output of the camera tube to the deflection circuits. De ilection signals are applied to the camera tube to scan the image across the aperture at a rate which is high relative to the expected rate of vibration, and the value of the deflection signal is measured at the instant the optical discontinuity crosses the aperture and from this instantaneous measurement of the deflection signal an information signal is derived which is indicative of the position of the image at that instant..

This invention relates to an electro-optical device or system adapted for use as a displacement indicator.

The device or system of the invention is especially adapted for use as a means for detecting. observing and/or measuring displacement or position, particularly smallamplitude high-speed displacement, as for example, vibration of a physical body. The device may also be used as a curve tracer, and as a component of a tracking system.

The device or system of the present invention is different in signicant respects and is to be distinguished. from prior art devices and systems of which I am aware. One type of such prior art system is the one in which the output of the image dissector tube is fed back to the deflection plates to hold the optical discontinuity (between the dark and bright portions of the image) at the aperture of the tube. This type relies on feedback or servo-loop signals.

In contra-distinction to the servo type, the device or system of the present invention does not employ servosystem techniques. There is no feedback from the output of the camera tube to the deflection circuits,

In the device or system of the present invention, deilection signals are applied to the deflection coils (or deflection plates) of the camera tube to scan the image across the aperture. There is no attempt to maintain or hold the image at the aperture. The rate or frequency of scanning is preferably, but not necessarily, made high relative to the expected rate or frequency of vibration or movement of the body or other target being observed. The value of the deflection signal is measured at the instant the optical discontinuity (which separates the dark area from the bright) crosses the aperture, and from this instantaneous measurement of deflection signal, an information signal is derived which is indicative of the position of the image at that instant. Thus, vibrational and other high speed movements of a body or other target may be observed and measured.,

A principal object of the present invention is, then, to provide an improved electro-optical device or system Patented Feb. 10, 1970 for detecting. measuring. observing and/or indicating displacement or position of a target.

Another object is to provide such a system in which the control panel is separate from the optical head, thereby allowing for remote control and operation.

A further object is to provide such a system which is of minimum size and weight.

Another object is to provide an electro-optical displacement measuring system in which the optical head is isolated from the control system.

Another object is to provide a system of the above type in which an electronically reproduced image appears on the control panel for ready viewing by the operator.

Another object is to provide a system of the above type in which high-speed switching systems, functioning in a hybrid analog-digital mode, are employed to monitor positions of the optical targets.

Another object is to employ time-sharing principles and techniques to sequentially sample and memorize the successive positions of the optical discontinuities forming the targets.

Another object is to provide an electro-optical displacement measuring system which is not dependent on the functioning of a servo loop.

The invention will be clear from a consideration of the following detailed description and accompanying drawings in which:

FIG. 1 is a block diagram of an electro-optical displacement indicating system embodying the present invention in one form;

FIG. 2 is a diagram of a known form of camera tube of the image dissector type;

FIGS. 3, 4, and 5 are diagrams of electron targets on the'aperture plate when the target is in three different positions;

FIG. 6 shows representative waveforms at various points in the system;

FIG. 7 is a schematic of the level detector 40 of FIG. l;

FIG. 8 is a schematic of the switch control flipflop 60 of FIG. 1;

FIG. 9 is a schematic of the first switches 80, the storage system 100, and the second switches of FIG. l;

FIG. 10 is a diagram of a multiple target;

FIG. l1 illustrates the waveform of the cameratube output signal during scanning of the multiple target;

FIGr l2 is a schematic of the level detector 302 and secondary target inhibit 301 of FIG. 1; and

FIG. 13 is a schematic of the vertical deflection drive 31 and disable circuit 329 of FIG. l.

Referring now to the drawings, FIGURE l is a block diagram of a complete displacement-indicating system which includes not only the basic system of the present invention but also a. number of additional or optional features.

In FIG. l, the basic system includes the camera tube 20. preferably a photo tube of the image dissector type, the level detector 40. the flip-flop switch control 60. the first switches 80, the storage system.100, the second switches 120. the output amplifier 140, and an output such as the display device 160.

One suitable form of camera tube 20 is illustrated diagrammatically in FIG. 2. This is a known form of image dissector tube having the usual energy-sensitive photocathode 2l, accelerating electrode 22, focusing electrode 23, image shield 2S with central aperture 26, and electron multiplier section 27. A lens 28 focuses the target 200 on the photocathode 21.

In FIGS. 1 and 2, the camera tube 20 is illustrated as provided with vertical deflection coils 24 and also with horizontal deflection coils 29. Deflection currents to the vertical coils 24 are derived from a vertical oscillator 32 and delivered by the vertical deflection drive 31. l-lorizonA tal oscillator 33 and horizontal deflection drive 34 provide thenecessary deflection currents to the horizontal de` flection coils 29.

A manually controlled relay or electronic switch 3S controls whether deflection currents are applied to one or to the other or both the vertical and horizontal coils 24 and 29.

The deflection currents may also be applied, as by way of leads 210 and 211, to a monitor cathode ray tube dis play device 212.

The high voltage power supply 223 supplies the necessary high voltage to the electron multipler section 27. This power supply 223 is preferably controlled by a signal derived from the output of the camera tube 20 so as to compensate for variations in ambient light, Image power supply 222 supplies the voltage to the image section of the camera tube 20` In a typical case, the target 200 would be a piece of work whose high-speed vibration, displacement, or other movement is to be detected. observed and measured. In stich case, the image dissector tube 20 would be focussed, for example, on the edge of the work. However, in describing the present invention, it will be convenient to assume that the target is a work piece of rectangular shape the upper half of which is white and the. lower half of which is black, as illustrated in FIGS. l and 2. The image dissector tube 20 is focussed on the optical discontinuity or botindary line 203 between the light area 201 and the dark area 202. The optical image of the work is focused on the photocathode 21 of the image dissector tube 20 by the lens 28, and an electron image is emitted from the inner surface of the photocathode 21 and focused on the image shield 25. The electron image 200e of the target 200, when the beam is centered vertically, is illustrated in FIG. 4. It will be seen that the optical discontinuity or boundary line 203 goes through the aperture 26.

In accordance with my present invention, the electron image of the black and white target 200 is deflected vertically up and down across the aperture 26, at a repetition rate which may be high relative to the expected rate of target vibration or other movement to be detected. As a result, the electron image at the aperture 26 changes from the half-white half-black image 200C of FIG, 4. to the all black image 2001) of FIG. 3 as the electron image is moved up, then to the all white image 200d of FIG. as the electron image is mor-led down, The rate of tite up and down movement corresponds to the vertical deflection frequency, as controlled by oscillator 32.

As a result of the aforementioned vertical deflection of the electron image, the output of the electron multiplier section 27 of the image dissector tube 20 changes from a high level to a low level and then back to a high level as the electron image at the aperture 26 changes from all white to all black and then back to all white A finite period of time is required for the optical discontinuity or boundary line 203 of the electron image to move across the aperture 26 and, accordingly, the waveform of the output of the photo tube has the shape indicated in FIG. 6(a) in which the high level white signal and low level black signal are connected together by steeply sloping lines, representing the change in output which occurs as the optical discontinuity 203 of the electron target moves across the aperture 26` Referring again to FIG. 1, the function of the level detector 40 is to convert the waveform of. FIG. 6(a), into a rectangular pulse waveform.

It will be helpful in explaining and understanding the present invention to describe the outputs of the various components of the basic system at an instant when the target 200 has been displaced from its normal position. Assume an instant when the target has been displaced upward, and the electron image at the aperture 26 is as shown in FIG. 3. The outputof the camera tube 20 will then be as indicated graphically in FIG. 6(b`l As there shown, the output signal will be at the dark; level for 4 most of the deflection cycle, and at the light level for only a relatively small part of the cycleA Assume that the level detector 4() has been adjusted to oe triggered by an output value corresponding to that represented by the dot on the upward slope of the waver'orni of FIG. 6(b`). In such case. the level detector is triggered and produces an output pulse, such as is represented graphically in FIG. 6(c'). This is a pulse with a steep leading edge. The leading edge is positive going, assuming the level detector 40 has been set b v adjustment 42 (FIG. l) to operate in the black-to-white mode. If set by 42 to operate in the white-to-black mode, the leading edge of the output pulse of the level detector will be negative going. It will be assumed that the adjustment 42 is set to operate in the black-to-white mode.

The switch control circuit is a flip-flop having. when in a stable state, a high level output and a low level output, one on lead 61 and the other on lead 62. Which of the leads has the high level output, and which the low, depends upon the state of the flip-flop 60. In FIG. 6, the waveform titdl represents the signal on lead 6l, while waveform 6(e) represents the signal on lead 62Y The signals on leads 61 and 62 are applied, respectively, to a first pair of electronic switches 81 and 82, preferably transistor switches. Since one signal is high and the other low, one of these transistor switches will close (the transistor will conduct) and the other will open (the transistor will be cut oil). It will be assumed that the circuit has been so arranged that a high level signal closes the switch (the transistor conducts) and a low level signal opens the switch (the transistor is cut off). Thus, at time l1 the signal of FIG. 6(11) will close transistor switch 81 and the signal of FIG. 6ta) will open transistor switch 82.

Referring again to FIG. l, the vertical deflection signal, shown graphically in FIG. 6U), is applied by way of lead 36 to the first pair of transistor switches 81 and 82 in parallel and then to the storage system 100. Storage system comprises capacitors 101 and 102. Capacitor 101 is connected across the circuit which includes transistor switch 81 in series. Capacitor 102 is connected across the circuit which includes transistor switch 82 in series. If the switch, 81 or 82, is closed, the deflection signal is applied through the switch to the storage capacitor. One of these switches is closed, the other is open. Which one is closed. and which one is open, depends on the state of the flip-flop 60. The time constants are so selected that the storage capacitor will follow the vertical deflecting signal.

Storage capacitors 101 and 102 are conected through a second pair of transistor switches 121 and 122, respectively, into a common output amplifier 140. If the second transistor switch, 121 or 122, is closed, the capacitor signal passes through and is applied to the out put amplifier 140. lf the switch. 121 or 122. is open, the capacitor signal does not pass through. One of the switches 121, 122 is open, the other closed. Which one is open and which one closed depends upon the state of flipflop 60. Switch 122 is always in the same condition as switch 81, and switch 121 is always in the same condition as switch 82.

Transistor switches 81 and 121 are connected in series, and switches 82 and 122 are connected in series. The storage capacitor 101 is connected between the common junction point of switches 81 and 121 and ground. The storage capacitor 102 is connected between the common junction point of switches 82 and 122 and ground.

Thus, when the first switch of one series pair of switches is closed, allowing the capacitor to follow the input signal, the second switch of the series pair is open. At this time. the rst switch of the other series pair is open and the second switch of the pair is closed. Thus. the capacitor signal is applied through the second switch to the output amplifierV sinapsi In FIG. 6, the waveform tg) illustrates the signal on the output side of storage capacitor 101` and wave` form 6(11) illustrates the signal on the output side of storage capacitor 102. Note that at time I1, the signal level on output lead 61 of ip-flop 60 goes high (waveform 6(d)) while the signal level on output lead 62 goes low (waveform 6(e) As a result, transistor switches 81 and 122 close, while switches 82 and 121 open. The vertical scaning signal on lead 36 passes through transistor switch 81 into storage capacitor 101, and storage capacitor 101 follows the scanning signal. Transistor switch 121, on the output side of capacitor 101 is open, and no signal passes to the output amplifier 140. The signal developed across capacitor 101 is illustrated in FIG. 6 as waveform 6(g).

As mentioned above, at time t1, when the signal level on output lead 62 of flipflop 60 goes down, transistor switches 82 and 121 open, i.e., become non-conductive. The vertical scanning signal on lead 36 is now blocked from storage capacitor 102 by the open switch 82, but the instantaneous signal which appeared across capacitor 102 at the instant switch'82 opened (i.e. the capacitor signal at time Il) is now applied through the closed switch 122 to the output amplifier 140. The capacitor 102 sees a high impedance circuit and the instantaneous signal which is across the capacitor at time r1 is substan tially maintained for the period of the vertical deflection cycle. This signal is illustrated in FIG. 6 by that portion of the waveform 6(11) which is identified as signal S1 extending from time t1 to time r2.

At time t2, in response to the signal from level detector 40, the flip-flop 60 changes its state and the signal on output lead 61 goes down while the signal on output lead 62 goes high. Transistor switches 82 and 121 now close (conduct) while switches 81 and 122 open (nonconduct). Storage capacitor 101, at instant t2, had a signal thereacross corresponding to the instantaneous value of the vertical deflection signal at that instantg This signal, identified as S2 in FIG. 6(g) is applied by capacitor .101 through closed switch 121 to the output amplifier 140.

The output signal from amplifier 140 is illustrated in FIG. 6 as waveform 6(1'). It will be seen that waveform 6(1') is made up of signals derived alternately from storage capacitors 101 and 102. A filter, identified in FIG. l, as response-time adjustment 141 is used to take out the switching transients which would otherwise exist in the amplifier output signal at time instants corresponding to the time instants when the flip-flop switch control 60 is changing from one state to the other.

In FIG. l, the output from amplifier 140 is shown applied to a display device 160, ordinarily a Cathode ray tube, and to a signal channel 161 which may utilize the signal for any of a wide variety of purposes.

It will be seen that the output signal from amplifier 140 is derived from and corresponds to the instantaneous vertical deflection signal at the instant the optical discontinuity or boundary line 203 crosses the aperture 26. If the target 200 is vertically motionless at the mid-point of the scanning range the boundary line 203 of the vertically detlecting electron image will cross the aperture 26 at the mid-point in the vertical deflection cycle. 1f the target 200 moves upward from its normal position, the boundary line 203 of the election image will cross the aperture 26 closer to the upper peak of the deflection cycle. If the target 200 moves downward from its normal position, the boundary line 203 will cross the aperture 26 closer to the lower peak of the deflection cycle.

Thus, the level of the output signals from the storage capacitors 101 and 102 will vary according to the vertical position of the electron image, and the waveform of the output signal from output amplifier 140 will be proportional to the vertical movements of the target 200.

As indicated previously hereinbefore, the frequency of the vertical deflection cycle is preferably selected to lbe high relative to the expected rate ot' vibration or other movement of' the target. The phase of the switching varies as the position of the target changes within the tleld of view. Since, for any target. the phase error is never more than plus or minus l80, the frequency is the same. This however is of no consequence as the final output signal is Still an analog of the target displacement regardless of the repetition rate of the individual samples. Of course, when the same system is used for target movements at frequencies near to or above the scan frequencies, the targets displacement waveform will be reproduced but on a different time scale. This time scale will be referenced to the scan frequency. In this way, the usefulness of this system can be extended to 200,000 c.p.s. of displacement movements.

The foregoing describes the basic system for detecting movement of the target in one direction. The detection of movement in the vertical direction has been described, since this is perhaps the most common direction of vibrational movement. Similar techniques can of course be used to detect movement in the horizontal direction, in which Case the horizontal deflection signal is used instead of the vertical I ed movements which include both "mh the horizontal and vertical deflection signals may be used at once. For example, if We desire to determine the vertical displacements of a vibrating rod at various places along its length so as to determined nodal points, etc., or if we desire to use the device as a curve tracer, we may use a high frequency vertical scan combined with a slow horizontal ramp scan.

The system illustrated in FIG. l includes a number of features which are optional and in addition to the basic system. These will now be briefly described.

In FIG. l, a level detector 142 is shown coupled to the output of amplier 140. This level detector 142 iS adjustable. It may be triggered by either positive (-l) or negative signals, as indicated by adjustment 143, and it may be set to respond to input signals which are either less than or greater than a selected value, as indicated by the adjustment 144. lf, for example, the output from amplifier 140 exceeds a selected value1 the level detector 142 will deliver a signal to the display device 145, which may be a warning light, or an alarm signal may be sent out over lead 146.

Level detector 242 has a generally similar function with respect to the output from the photo or camera tube 20. If the signal output of photo tube 20 exceeds a selected value, the level detector 242 will be triggered and will actuate display device 24S, which may be an alarm device to give warning that too much signal is being delivered as a result of excess illumination on the target. The intensity control of the monitor cathode ray tube 212 may also be connected to the camera tube output, much as in a closed-circuit television system.

The foregoing features, involving level detectors 142 and 242 are of practical commercial importance but are relatively unimportant so far as the present patent application is concerned.

Of considerably greater importance from a patent aspect is the feature of the system of FIG. l which allows the movement of a plurality of targets to be detected and observed. The details of how this feature is accomplished will be described later. First, a description will be given of the circuit details of some of the components of the basic system which have been shown in block form in FIG. l, such as the level detector 40, the flip-flop Switch control 60, the first pair of transistor switches 80, the storage system 100 and the second pair of transistor switches 120.

Referring now to FIG. 7, this is a schematic diagram l of a suitable form of level detector of FIG. l. The sigv 75 `nal from the electron multiplier section 27 of the image dissector tube 20, for example, the signal of FIG. tbl. is supplied on lead 52 to the base of a first transistor 43. The first transistor functions as an emitter follower and enables the input signal to look into a relatively high impedance. The adjustment of potentiometer 44 controls when the second transistor 45 will conduct. The output or' transistor 45 is a generally square pulse signal which is applied to a wave shaper and amplitude-swing control circuit comprising the transistors 46, 47 and 484 The output of transistor 48 is a negative pulse (shown on lead 51) which is inverted by transistor 49 to produce the positive pulse on lead 50. This positive pulse is illustrated as pulse 6(c) in FIG. 6. By adjusting switch 42 of FIG. 1 to the white-to-black mode instead of the black-to-white mode, the negative pulse on lead 51 (FIG. 7) may be selected instead of the positive pulse on lead 50.

FIG. 8 is a schematic diagram of a suitable form of buffered flip-flop switch control circuit 60. The positive pulse on lead 50 of FIG. 7 is applied through diodes 53 and 54 to the bases of flip-flop transistors 55 and 56,

thereby turning on" the transistor which was offj' and turning "of the transistor which was on Transistors 57 and 58 function as buffers. and the output signals from transistors 57 and 58 appear on leads 61 and 62` When the signal level on lead 61 is high (+12 v.), the signal level on the other lead 62 is low (ground), and vice versa.

FIG. 9 is a schematic of a suitable circuit for the rst pair of transistor switches in block 80, storage system in block 100, and second pair of transistor switches in block 120 of FIG. 1. Assume that the time corresponds to time t1 of FIG. 6. The high level signal illustrated in FIG. 6(d) on output lead 61 of flip-flop 60 is applied (FIG. 9) via diodes 63 and 64 to transistor switches 81 and 122 and these transistors turn on The low level signal on lead 62 is blocked by diodes 66 and 67, and accordingly, transistor switches 82 and 121 are ofl The vertical deflecr tion signal on lead 36 of FIG. 1 is applied to a buffer stage 83 and thence, via level adjusting potentiometer 84 to switch transistor 81. Since switch transistor 81 is at this time conducting, the deflection signal is applied through transistor 81 to storage capacitor 101, and the voltage across capacitor 101 follows the deflection signal.

The vertical deflection signal is also applied to the switch transistor 82 but switch transistor 82 is at this time non-conducting.

When, at time r2 of FIG. 6. the flip-flop 60 changes its state. the voltage level on lead 62 rises to high and the level on lead 61 drops to low. The high leve] signal on lead 62 now passes through diodes 66 and 67 to turn on switch transistors 82 and 121. The other two switch transistors 81 and 122 now turn oil.

At the instant t2 that switch transistor 81 was turned off, the voltage across capacitor 101 corresponded to the value of the vertical deflection signal at that instant. Transistor 101 looks into a high impedance buffer stage 184 and applies to switch transistor 121 a signal corresponding to the deflection signal at time 12. Since transistor 121 is conducting, the signal is passed therethrough to the output amplified 140 comprising transistors 147 and 148.

It was stated previously hereinabove that the basic concept of the present invention may also be embodied in a system for tracking or detecting a multiplicity of targets each of which is in the field of vision of the camera tube.

`Such a system will now be described.

To illustrate how the system operates to detect the multiplicityl orr targets. it will be convenient to consider merely a single target having a plurality of horizontally disposed black and white stripes. The electron image of such a target is illustrated in FIG. 10. Assume that in FIG. l() the electron target is shown deflected fully upwardly, i.e., in the position it would acquire at the upper peak of the vertical scan cycle. At this instant, the aperture 26 is in a lower allawbite area. The optical discontinuity or boundary line between each of the black and white areas, moving from black to white are identified in FIG. by the reference numerals 314 315, 316 and 317. It will be assumed that the selector switch 42 (FIG. l) is set to the blacktowhite position so that level detector 40 is triggered, as at the dot position of FIG. 6(b), as the output signal from the camera tube rises from the black to the white level.

It will be seen that when the electron image of FIG. 10 is deflected downwardly by the vertical deflection signal, a series of optical discontinuities will move across the aperture 26, and the level detector will be triggered successively by each signal developed as the black-to-white discontinuities 314-317 pass across the aperture 26. The waveform of the output signal of the photolube 20 during the downward scan is illustrated in FIG. 11.

Assume now that it is desired to track or detect the rst three optical discontinuities only, namely, the discontinuities 314, 315 and 316, and to ignore the optical discontinuity at 317. In such case, the pulse counter 300 (FIG. l) is set by the number adjustment 311 so that the pulse counter delivers an output signal after counting three pulses.

The pulse output from pulse counter 300 is applied as a disable pulse by way of lead 319 to the secondary target inhibit circuit 301 to disable the tracking system. It does this by causing circuit 301 to connect to ground the output lead of level detector 40. The circuit 301 is used only during tracking or detecting of multiple targets, and is connected into the system as by closing manually switch 318. The grounding of lead 50, in response to the disable pulse on lead 319, prevents the output of the level de tector 40 from reaching the flip-flop switch control circuit 60. Thus, until the ground connection is removed from lead 50, no change will occur in the flip-flop switch control circuit 60. Hence, in the present illustration, when the optical discontinuity 317 crosses the aperture 26, the system will be insensitive thereto.

It will be observed that, in the present example, when the electron image of the horizontally striped blackand white target is detlected upwardly across the aperture 26 on the return trace of the vertical scan, ythe cantera tube 20 will detect black-to-white discontinuities at boundaries 327, 326, 325 and 324 in FIG. 10. Since it is desired that the system be responsive only to the optical disconn tinuities at 314. 315 and 316 and to be non-responsive to all other optical discontinuities, the vertical deflection drive 31 is provided with a disable subcircuit 329 by means of which a disable signal is delivered, on lead 330 of FIG. 1 to the secondary target inhibit circuit 301 during vertical retrace to assure that circuit 301 maintains a ground connection to output lead 50 of level detector 40, -thereby to assure that the tracking or detecting system is disabled during vertical retrace (which in the present example moves the electron image upward across the aperture 26).

At the end of the vertical retrace, the electron image again starts its downward movement. The vertical deflection signal is supplied by way of leads 36 and 304 to the level detector 302. When the magnitude of the den flection signal rises to ra suflicient value. as controlled by adjustment 306, an able pulse is delivered by the level detector 302 to the secondary target inhibit circuit 301 to reset the inhibit circuit, thereby to remove the ground from the lead 50. This enables the flip-flop switch control circuit to be triggered at point 314 (FIG. 11) by the pulse which results from the optical discontinuity 3'14 (F-IG. 10). The action described above is then repeated.

It will be seen from the foregoing description that the system of FIG. 1 is capable of tracking or detecting a plurality of discontinuities, each of which appear in the field of vision of the camera tube 20. The detecting of three discontinuities 314, 315, 316 has been described. The output signal from output amplifier 140 for each of the three discontinuities 314, 315 and 316 is developed in a manner identical to that described hereinbefore with respect to the basic system. The magnitude of the output signal developed for each optical discontinuity 314, 315 and 316 corresponds to the instantaneous magnitude of the vertical deflection signal, i.e., the magnitude of the deflection signal at the instant the optical discontinuity crossed the aperture 26. Three separate output signals are developed which, when displayed on the display device 160, appear iat three separate levels, corresponding to three different instantaneous values of deflection signal. Thus, if the three discontinuities are capable of separate and independent vibration or other independent vertical movement, each of the three movements may, by the system shown and described, be independently detected.

The pulse counter 300 is a known yform of pulse counter, and the circuit details thereof need not be described.

Suitable circuits for the level detector 302 and the secondary target inhibit 301 are shown in FIG. 12, and a suitable circuit for the ver-tical retrace disable circuit 329 is shown in FIG. 13.

Referring now to FIG. 12, the level detector 302 comprises the transistors 343, 345, 346, 347 and associated circuitry. The vertical deflection signal is applied by way of lead 304 to transistor 343 which is adjustably biased by potentiometer 344. When the magnitude of the deflection signal rises to a sufficient value, the transistor 343 conducts and transistor -345 turns off. The signal developed at the collector of transistor 345 is applied to 1a wave shaper comprising the transistors 346, 347, andthe output signal developed on lead 305 is used as the able signal which in FIG. 1 is shown applied to the secondary target inhibit circuit 301 to remove the ground connection from lead 50.

Referring again to FIGS. 1 and 12, the secondary target inhibit circuit 301 comprises the flip-flop transistors 351 and 352, the butler transistors 353 and 354, the switch transistor 355, and associated circuitry. When la disable pulse is received on lead 319 from the pulse counter 300, the right transistor 352 of flip-flop 351, 352 is turned on," transistor switch 355 is turned on" and lead 356 is connected to ground through transistor switch 355. Thus, if manual switch 318 is closed, lead 50 is connected to ground through a low impedance circuit and level detector 40 is thus isolated from flip-flop switch control 60. This condition continues until the flip-flop 351, 352 of the circuit 301 is caused -to shift to its other state by the application of an able pulse on lead 305 from level detector 302. As already indicated, level detector 302 is responsive to the magnitude of the vertical deflection signal which is applied thereto on lead 304.

Referring now to FIGS. 1 `and 13, lthere is shown in FIG. 13 a suitable circuit for the vertical deflection drive 31 land circuit 329 for producing a disable signal on retrace for application to the secondary target inhibit circuit 301. Timing pulses for controlling the vertical rate of scan are developed by the R-C circuit comprising resistor 331 and capacitor 332 which causes the unijunction transistor 333 to conduct vat regular intervals to discharge the capacitor 332. The timing signal developed across capacitor 332 is applied by way ofthe capacitor 334 to la waveshaper transistor 335, and the pulse signals developed across transisor 335 are applied by way of lead 336 to the flip-flop 337 comprising the transistors 338 and 339. The transistors 340 and 341 function as buffers. yIt will be seen that the flip-flop 337 changes its state at a rate and in time coincidence with the timing pulses developed -in the timing circuit, and yields, in conjunction with a secondary flip-flop 437, a signal during retrace which is applied as a disableon-retrace signal to transistor 353 of the secondai y target inhibit circuit 301 to turn on the right transistor 352 of flip-flop 351. thereby to turn on the switch transistor 355, and thereby to yassure that the leads 356 and 50 are maintained at ground during the retrace portion of the vertical scan cycle.

It will be seen that by adjustment of level detector 302 (at a time when the target is in its normal position), the optical discontinuiiy 315 (or 316) may be selected tas the first discontinuity to be detected, instead of 314. Also, in such case, by sett-ing pulse counter 300 to count one pulse (instead of three as described in the example given above) the system may be used to track or detect the single discontinuity, such as 315, out of the multiplici-ty of discontinuities appearing before the camera tube.

In describing the system of the present invention, l have assumed, for the most part at least, that the target movements to be detected were in the vertical direction. However, as previously indicated above, the system may, of course, also be used to detect target movements in the horizontal direction, or for that matter, target movements in a direction having both vertical and horizontal components.

Also, while I have illustrated and described specific components and circuitry for accomplishing the desired tracking or detecting, obviously variations in such components and circuitry, and in the use to which such circuitry is put, are possible without departing from the basic concept of my invention as defined in the claims which follow.

What is claimed is:

1. Apparatus for detecting displacement of a target, said apparatus comprising: a camera tube for providing an electron'image of at least that part of the target having an optical discontinuity between areas of substantially different light reflectivity, luminosity or transmissibility, said camera tube having an aperture through which the electrons of said electron image pass, and means for developing a camera-tube output signal which varies with the quantity of electrons passing through said aperture; means for developing a deflection signal for deflecting said electron image back and forth across said aperture for changing the level of said output signal when said optical discontinuity crosses said aperture; a bistable circuit having first and second output terminals, one of which has a high level signal and the other of which has a low level signal according to the state of said bistable circuit; means for applying the output `signal of said camera tube to said bistable circuit to trigger said circuit from one stable state to the other in response to change in the level of the camera-tube output signal; first and second storage capacitors; rst and second electronic. input switches coupled to said first and second storage capacitors respectively; first and second electronic output switches coupled to said first and second storage capacitors, respectively; means for coupling said first and second output terminals of said bistable circuit to said first and second input switches, respectively, and means for coupling said first and second output terminals of said bistable circuit to said second and first output switches, respectively, for controlling the conditions of said input and output switches according to the state of said bistable circuit, whereby one of said input closed andthe other of said input switches and the one of said output switches are open, according to the state of said bistable circuit; a common output circuit; means for coupling said first and second output switches to said common output circuit; and means for applying said deflection signal to said first and second input switches in parallel whereby one of said storage capacitors receives the deflection signal and the other does not and whereby said other of said storage capacitors deu livers its signal to the common output circuit and said one does not, the signal delivered to said output circuit corresponding :o the magnitude of the deflection signal at the time said optical discontinuity crosses said aperture.

2. Apparatus as claimed in claim 1 characterized in that an adjustable level detector circuit is inserted between the outpu: of said camera tube and said bistable circuit for detecting the level of the camera-tube output signal and for responding to a selected level, thereby to determine the instant at which said bistable circuit is triggered.

3. Apparatus as claimed in claim 2 further characterized in that said camera tube is of the image dissector type and has an electron multiplier section.

4. Apparatus as claimed in claim 3 further characterized in that the means for developing a deflection signal are means for developing a vertical deflection signal.

5. Apparatus as claimed in claim 4 further characterized in that said bistable circuit is a flip-flop circuit.

6. Apparatus for detecting displacement of a target, said apparatus comprising: a camera tube focused to produce an electron image of at least that part of the target which provides an opfical discontinuity between areas of substantially different light reflectivity, luminosity or transmissibility for developing a camera-tube output signal which varies with the electron image focused on said camera tube; deflection signal means for detlecting said focused electron image in a reciprocating manner for changing the level of the camera-tube output signal as a function of the position of the optical discontinuity; and means coupled to the output of said deflection signal means and also to the output of said camera-tube for referencing the camera output signal to the deflection signal for determining the instantaneous values of said deflection signal at the times of said changes in said camera-tube output signal, thereby to detect changes in the position of said target; said apparatus characterized in that said electron tube is of the image dissector type having an aperture through which the electrons of said focused electron image pass.

7. Apparatus as claimed in claim 6 further characterized in that said camera tube has an electron multiplier section, in that an adjustable high voltage power supply is provided connected to said electron multiplier section, and in that means are coupled between said camera tube output and said high voltage power supply for adjusting said voltage as a function of the output of said camera tube, thereby to compensate for variations in ambient light.

8. Apparatus for detecting displacement of a target, said apparatus comprising: a camera tube focused to produce an electron image of at least that part of the target which provides an optical discontinuity between areas of substantially different light reflectivity, luminosity or transmissibility for developing a camera-tube output signal which varies with the electron image focused on said camera tube; deflection signal means for deflecting said focused electron image in a reciprocating manner for changing the level of the camera-tube output signal as a function of the position of the optical discontinuity; and means coupled to the output of said deflection signal means and also to the output of said camera-tube for determining the instantaneous values of said deflection signal at the times of said changes in said camera-tube output signal, thereby to detect changes in the position of said target, said means coupled to the output of said deflection signal means and also to the output of said camera tube including electronic switch means responsive to said camera tube output signal for controlling the passage therethrough of said deflection signal, signal storage means for receiving the deflection signal passing through said electronic switch means, and output means coupled to said storage means for delivering an output signal correspond- .ing to the magnitud@ of said deflection signal at the instant said electronic switch means open to block passage of said deflection signal to said storage means.

9. Apparatus as claimed in claim 8 characterized in that said signal storage means receiving said deflection signal is adapted to develop a signal which follows closely said deflection signal, thereby 'to deliver an output signal which corresponds closely to the deflection signal at the instant said electronic switch opens.

10. Apparatus as claimed in claim 9 characterized in that said deflection signal means includes means for de-l flecting said focused electron image along both the vertical and horizontal axes, and further characterized in that said means for determining the instantaneous values of the deflection signal are means coupled to the deflection signal means for one of said axes only.

11. Apparatus as claimed in claim 8 further characterized in that a bistable circuit is inserted between said electronic switch means and the output of said camera tube, and in that said switch means comprises a pair of electronic switches so coupled to said bistable circuit that one of said switches is in one condition and the other is in the opposite condition according to the state of said bistable circuit; further characterized in that said sgnal storage means comprises a pair of capacitors, one connected to each switch; and further characterized in that the coupling between said storage means and said output means includes a pair of electronic output switches coupled to said bistable circuit so that one of said output switches is in one condition and the other in the opposite condition according to the state of said bistable circuit.

12. Apparatus as claimed in claim 11 further characterized in that inhibit means having two stable conditions are provided coupled to the input of said switch-control bistable circuit for inhibiting selected output signals of said camera tube from changing the state of said switch-control bistable circuit, and signal counter means coupled between the output of said camera tube and said inhibit means for placing said inhibit means in condition to inhibit after a selected number of output signals have been delivered from said camera tube.

13. Apparatus as claimed in claim 12 further characterized in that means are provided coupled between said deflection signal means and said inhibit means for placing said inhibit means in condition to inhibit camera-tube output signals from reaching said switch-control bistable circuit during the retrace portion of the deflection cycle.

14. Apparatus as claimed in claim 13 further characterized in that level detector means are coupled between said deflection signal means and said inhibit means for changing the condition of said inhibit means to allow camera-tube output signals to reach said switch-control bistable circuit.

15. Apparatus as claimed in claim 14 further characterized in that an adjustable level detector circuit is inserted between the output of said camera tube and said bistable switch-control circuit for detecting the level of the camera-tube output signal and for determining the instant at which said bistable circuit is triggered.

References Cited UNITED STATES PATENTS 2,970,187 l/l961 Hinton 178-6-8 3,010,024 11/1961 Barnett et al. Z50-203 3,281,601 10/1966 Sheftelman 250-203 3,120,578 2/1964 Potter et al 250-203 X RALPH G. NILSON, Primary Examiner T. N. GRIGSBY, Assistant Examiner U.S. Cl. X.R.

iUNITED STATES PATENT OFFICE Patent Nc.

Inventor(s) Robert Starer Dated February lO, 1970 It is certified that error appears in the above-identified' patent and 4that; said Letters Patent are hereby corrected as shown below:

insert --swtch are-- l Claim l, at the end of line 66, after "input" es and the other of said output switches .SIGNED MWD SEALED i Aus 1 11970 

